Whitespotted Rabbitfish Research Articles

An Investigation on the Morphometric Characteristics of the White-Spotted Rabbitfish (Siganus canaliculatus Park, 1797) in the Small Semi-Enclosed Bay Based on Truss Morphometric Methods

An Investigation on the Morphometric Characteristics of the White-Spotted Rabbitfish (Siganus canaliculatus Park, 1797) in the Small Semi-Enclosed Bay Based on Truss Morphometric Methods

Genetic Diversity of White-spotted Rabbitfish (Siganus canaliculatus) on Different Seagrass Habitats in Inner Ambon Bay, Indonesia Based on Mitochondrial CO1 Sequences.

This study aims to analyse the genetic diversity of Siganus canaliculatus in the Inner Ambon Bay (IAB) waters. DNA of S. canaliculatus specimens collected from IAB was extracted from tissues using a Tissue Genomic DNA Mini Kit, and partial CO1 genes were amplified using pair of universal primers. Genetic distances were determined by Kimura 2-parameter, and phylogenetic trees were constructed using the neighbour-joining method in MEGA 10.2.2 software. Arlequin software was used to analyse Fixation Index (Fst) and Analysis of Molecular Variance (AMOVA). There are three SNPs of S. canaliculatus from IAB that distinguish GenBank sequence data from S. canaliculatus. In Tanjung Tiram population group, contained three specific 677 (A), 679 (G), 703 (T) sites and two 693 (G), 714 (A) sites for the Nania population. Haplotype and nucleotide diversity of each population range from 0.000 to 1,000 and 0.000 to 0.004. Intra- and inter-population genetic differentiation were 21.19% dan 78.81%, respectively. Intra- and inter-population genetic distances were in range of 0.40-1.13 and 0.00-0.37, respectively. The pattern and direction of tidal currents as a link or barrier to spatial distribution and connectivity of S. canaliculatus larvae between seagrass habitats, as well as the presence of different anthropogenic pressures in each seagrass habitat, are thought to influence the genetic characteristics (genetic diversity, genetic variation, genetic differentiation and genetic distance) of S. canaliculatus populations in IAB waters. The results of this study provide information about the urgency of habitat-based fisheries management to support sustainable utiliation.s.

Growth and reproductive biology of white-spotted rabbitfish (Siganus canaliculatus) on different seagrass habitats in Inner Ambon Bay, Indonesia

Abstract. Latuconsina H, Kamal MM, Affandi R, Butet NA. 2021. Growth and reproductive biology of White-spotted rabbitfish (Siganus canaliculatus) on different seagrass habitats in Inner Ambon Bay, Indonesia. Biodiversitas 23: 273-285. Seagrass meadows are one of the important habitats for Siganus canaliculatus. This study aimed to compare the growth and reproductive biology of S. canaliculatus in different seagrass habitats on the Inner Ambon Bay. A fish sampling was observed once a month for a year (15 August 2018-20 July 2019) using a beach seine. The data analysis included growth patterns, condition factors, sex ratio, gonadal maturity, gonado somatic index, size at first maturity, and fecundity. The study results obtained body Length and weight varied between seagrass habitats, with an isometric growth pattern. The equation W: 0.0105 L3,1007 male and W: 0.0165L2,9444 female in mixed vegetation, while for monospecific vegetation, male W: 0.0109L3,0891 and female W: 0.0143L3,0067. The value of condition factors, sex ratio, size at first maturity, and fecundity differed between seagrass habitats. The range of fecundity is 198,000-783,750 eggs, and there is a positive relationship between body length and weight with fecundity. A technical approach to fisheries management is needed, namely: (i) the size at first maturity is used as a reference for the size of fish that can be caught, and (ii) determination of mixed vegetation seagrass as a conservation area; and monospecific vegetation as fishing grounds.

Reproduction of White-Spotted Rabbitfish (<i>Siganus canaliculatus</i> Park, 1797) in the Waters of the Buntal Island, Kotania Bay, West Seram-Mollucas

White-Spotted Rabbitfish (Siganus canaliculatus Park, 1797) are herbivorous fish that are associated with seagrass habitat and are widely distributed in mangrove and coral reef habitats. The waters of the Buntal Island – Kotania Bau have an ecosystem of seagrass medows, mangroves and coral reefs, with the association of S. canaliculatus as one of the target catch of fishermen. The purpose was study to analyze the biological aspects of S. canaliculatus, including: sex ratio, size of first maturity, and fecundity. The research was conducted from October 2015 until January 2016 in the waters of Buntal Island, Kotania Bay. Fish samples were collected from fishermen's catch using bottom gill nets and Set net. Each fish sample was dissected for sex determination and gonad maturity level. The analysis is used to see the relationship between body length and weight and fecundity. The results showed that 167 fish and 149 female fish. The ratio of male and female was balanced, namely 52.85%: 47.15% or 1.1: 1 (X2count 4.13 <X2table 11.34). The size of first maturity of female is 14.98 cm (14.5 - 15.5 cm) smaller than the male 18.9 cm (18.8 - 19.1 cm). The high potential of S. canaliclulatus based on the Fecundity obtained was in the range of 524,000 - 1,286,359 eggs. There is a positive relationship between body length and fecundity, indicating that the value of Fecundity increases with body size. To support its sustainable use in the wild, it is necessary to regulate the size of S. canaliculatus that can be harvest at a body length of > 15 cm TL, to provide opportunities for spawning and support population growth before exploitation, thus supporting responsible and sustainable fisheries.

Growth and Population Parameters of Panulirus penicillatus and Panulirus homarus in Labangka Tidal Waters, Indonesia

HighlightUtilization, Growth, and Population of Bullet Tuna (Auxis rochei Risso 1810) in Indian Ocean Southern Sumbawa (2020)Eligibility Status Kawakawa (Euthynnus affinis Cantor, 1849) from Lombok Strait and Indian Ocean Southern Sumbawa (2020)Biological Aspect of Parent Candidate of White-spotted Rabbitfish (Siganus canaliculatus) from Serewe Bay, Lombok Timur District (2020)Study of Sustainability in Management of Malabar Blood Snapper Fisheries in the Indian Ocean Coastal Waters, Sumbawa Regency (2020)Growth Rate and Survivorship of Acropora sp. Fragments that Transplanted on the Artificial Substrate Made from Fly Ash and Bottom Ash (2020)Reproductive Biological Aspect of Panulirus penicillatus in Sumbawa Island Waters, Indonesia (2019)Fisheries Resource Status of Spiny Lobster Panulirus penicillatus in Labangka Waters, South Sumbawa, Indonesia (2019)Growth Rate of Acropora formosa Coral Fragments Transplanted on Different Composition of Faba Kerbstone Artificial Reef (2019)Agribusiness of Edible Jellyfish Crambione mastigophora in Saleh Bay, NTB: Implementation of Sustainable Fisheries (2019)AbstractThe Labangka tidal waters, located south of Sumbawa Regency are the habitat and potential fishing ground for lobsters. The dominant species caught by the Labangka fishermen are the Panulirus penicillatus and P. homarus. Fishing pressure is one of the greatest factor influencing the biological and stock condition of lobsters in Labangka. The aim of this study is to determine the key attributes in growth and population parameters. Some attributes whose values are relatively stable compared to that of 2015, consist of conditional factors such as (old age), growth pattern (hypoallometric), growth coefficient (slow growth), exploitation rate (overexploited), and fishing rate (excessive fishing). While, attributes that have improved are carapace length at first capture (CLc) longer than 50% carapace length of infinity (0.5CL∞) and CL rate (CLc/0.5CL∞) reaching more than 1.00 (CLR > 1.00). In implementing sustainable management of spiny lobster for fishery resources, improvisation is needed in place of catching technologies. One of the recommendation is to add more fishing vessel (Lboat > 17.0 m) equipped with engines that are able to reach potential fishing ground in the west waters of Cemplung beach, Labangka.

First Record of Streaked Rabbitfish Siganus Javus (L., 1766) from the Iraqi Marine Waters, with Re Description of White-Spotted Rabbitfish Siganus Canaliculatus (Park, 1797)

Two Siganid fishes were described in the current study, the first one is Siganus javus (Linnaeus, 1766) as a new record and the other Siganus canaliculatus (Park, 1797), which was collected from the Iraqi marine waters. The samples were collected during December 2018. Streaked rabbitfish S. javus is diagnosed by a deep body, 54.01% in standard length, depth of caudal peduncle, 7.27%, total gill rakers 19 and silvery blue undulating lines on mid and lower sides of the body. Whereas the body depth of White-spotted rabbitfish S. canaliculatus was 39.08-42.66%, Caudal peduncle depth ranged from 5.21 to 5.66%, total gill rakers ranged from 22 to 24 and it is distinguished by a numerous pearly blue to whitish spots on the nape and trunk.

Aeromonas salmonicida isolated from wild and farmed fish and invertebrates in Oman

Aeromonas salmonicida was isolated from red spot emperor, king soldier bream, white-spotted rabbit fish and tilapia, and an invertebrate (abalone) in Oman during December 2011–May 2012. The cytotoxic enterotoxin ast gene was found widely distributed among the isolates; aerolysin-like protein (act) and the flagellin structural gene lafA less so; and the nuclease gene (nuc) not at all. However, there was not any evidence of pathogenicity among the isolates when tested in laboratory-based experiments using rainbow trout and Nile tilapia. Therefore, the risk of the pathogen to fish in Oman is unclear.

Điều tra hiện trạng nuôi trồng thủy sản lợ mặn cao triều ở xã Phú Mỹ, huyện Phú Vang, tỉnh Thừa Thiên Huế, Việt Nam

The marine high tide aquaculture status in Phu My commune, Phu Vang district, Thua Thien Hue province was studied from April to November 2017. The study had investigated 33 households on aquaculture, combing GIS techniques procedures with pond sites identified by GPS to create the attributes such as culture area, species, culture form, management and economic efficiency. The results had built the vector maps of all above aspects. The mainly cultured species in the region were black tiger shrimp, crab, rabbit fish and white-spotted rabbit fish with the form of polyculture (99.1%). Each species was stocked at different densities of 1.5 - 5 ind./m2 (black tiger shrimp) and less than 1 ind./m2 (fish and crab). These species were cultured from 2-3 cycles per year. Water treatment was not completed to implement with pollution factors. Waste water was not mostly treated. The efficiency of culture was low with 0.4 - 1 profit margin.

Bioaccumulation of heavy metals in marine fishes (Siganus sutor, Lethrinus harak, and Rastrelliger kanagurta) from Dar es Salaam Tanzania

Toxic metals that bioaccumulate and magnify along food chains are a concern to human health worldwide. This study determined heavy metal concentrations in three commercial fish species; viz: whitespotted rabbitfish (Siganus sutor), thumbprint emperor (Lethrinus harak), and the Indian Mackerel (Rastrelliger kanagurta) from Kunduchi fish market in Dar es Salaam, Tanzania, assessed potential risks to human health, and the suitability of their fins as a non-destructive monitoring organ. Metal concentrations in fish muscle differed significantly among fish species as a result of their diverse ecological needs, metabolism, feeding habits, and habitats. The results also indicated that fish fin may not be a very good non-destructive monitoring organ for most metals, but can be used selectively for some metals and fish species. The levels of metal intake (aluminum (Al), cadmium (Cd), copper (Cu), iron (Fe), lead (Pb) and zinc (Zn)) in fish muscles were below the FAO/WHO maximum levels for contaminants and toxins in foods for human consumption except for arsenic (As) which were higher than the recommended levels in Lethrinus harakand Rastrelliger kanagurta. It is recommended to reduce the amount of L. harakand R. kanagurta in daily meals of especially fishers and coastal communities who may eat fish up to three meals daily. Recommendation for further studies is provided.

Morphological, ultrastructural, and molecular description of Unicapsula fatimae n. sp. (Myxosporea: Trilosporidae) of whitespotted rabbitfish (Siganus canaliculatus) in Omani waters.

Investigations regarding the parasite fauna of wild whitespotted rabbitfish (Siganus canaliculatus) Park, 1797 revealed white, spherical, loosely attached cysts measuring 896 (375–1406) μm in diameter in the inner endothelial wall of the esophagus and stomach. Mature spores inside these cysts corresponded to the original description of spores belonging to the genus Unicapsula Davis, 1924. Unicapsula fatimae n. sp. spores were 6.23 (5.60–6.60) μm in length and 6.80 (6.12–7.39) μm in width. The length of large polar capsule was 2.62 (2.18–2.97) μm and width was 2.65 (2.32–2.90) μm, and the extended large polar capsule filament length was 15.50 (11.71–19.99) μm. Transmission electron microscope images of the plasmodia revealed a complex cyst structure that was unique among other Unicapsula spp. Ultrastructural details of the host–parasite interface and developmental stages of a species from the Unicapsula genus are described for the first time. Histology of an infected esophagus revealed some abnormalities and changes in the host tissue around the infection site, including hypertrophy of host esophagus epithelial cells and hyperplasia of host glandular tubules. The parasite presented here has been added to the genus Unicapsula using comparative morphological analysis and ultrastructural investigations supported by 18S small subunit ribosomal DNA molecular analysis.

Effect of different light regimes on the maturational progress of the whitespotted rabbitfish ( Siganus sutor )

In this study, the effects of different light regimes on the reproductive activity of a typical IndoPacific coral reef rabbitfish, Siganus sutor , were evaluated. Forty- five adult fish were exposed to nine different photoperiod (8L: 16D, 12L: 12D, 16L: 8D) and light intensity (1000, 2000, 3000 lux) combinations with three replicates and five other fishes reared under indoor light condition (Control). Gonadosomatic Index (GSI) and Hepatosomatic Index (HSI) were calculated after 60 days and compared among different experimental regimes in males and females. In the control group, GSI and HSI mean values were 4.67 and 3.24%, respectively, for females and 10.05 and 2.10%, respectively, for males, and these fish showed differences in comparison with the exposed fish. Females kept under 1000 and 2000 lux light intensities had a higher GSI mean value (9.26 and 10.39%, respectively) and also lower average HSI (2.10 and 2.31%, respectively) in 16L: 8D treatment. A similar result was also obtained for males, whereas the 3000 lux light intensity, 8L: 16D day length combination led to more gonadal development (GSIs of 16.41% in females and 12.03% in males). A comparison of results among different photoperiods also confirmed that maturation was induced better in fish maintained under 16L: 8D in both sexes. This investigation revealed the visible role of both photoperiod and light intensity on inducing maturity in the whitespotted rabbitfish, S. sutor . Thus, rearing of adults exposed to an artificial light regime, including 16L: 8D and 2000 lux light intensity, promotes more gonadal development than that occurring in the wild.

Trap Fishery and Reproductive Biology of the Whitespotted Rabbitfish Siganus sutor (Siganidae), within the Dar es Salaam Marine Reserves, Tanzania

Abstract—Fish samples and catch data were collected monthly from traditional basket fish traps set on reefs within the Dar es Salaam Marine Reserves (DMRs) to evaluate trap catch dynamics and reproductive biology of the rabbit fish Siganus sutor (Valenciennes 1835). Trap catch composition was 85% rabbitfishes by weight with a mean (± SE) catch per unit effort (CPUE) of 2.8 ± 0.1 kg trap-1 day-1 during a fishing season, which lasted between September 2004 and May 2005. CPUE did not differ significantly with lunar cycle, but exhibited a spatial variation, the highest being from Fungu Yasini Marine Reserve, which is further from shore. The spawning season of S. sutor is protracted, lasting between October and May, peaking in March. Size at first sexual maturity was 217.1 and 227.7 mm TL for male and female S. sutor , respectively. The species exhibits a size-dependent sex ratio, with a preponderance of females at larger sizes. The species shows high fecundity at a maximum of 1,300,400 oocytes for 396 mm TL female. Average (± SE) total fecundity was 627,052 ± 78,886 oocytes per female of 266 to 396 mm TL. It is proposed that beach seines be eliminated from the marine reserves and regulated trap fishery be allowed as a way to facilitate sustainable exploitation of the rabbitfishes and other reef fishes in the DMRs. Keywords: Trap fishery, rabbitfishes, Siganus, reproduction, marine reserves, Tanzania

Postsynaptic Alpha 2-Adrenoceptors Mediate Melanosome Aggregation in Melanophores of the White-Spotted Rabbitfish (Siganus canaliculatus)

The present investigation was undertaken to study the nature of neuro-melanophore junction in the white-spotted rabbit fish Siganus canaliculatus. In vitro experiments using split fin preparation indicated that melanophores of S. canaliculatus are highly responsive to potassium ions and adrenergic agonists. Potassium ions and the adrenergic agonists induced prompt melanosome aggregation that could be competitively blocked by yohimbine (alpha-2 specific adrenergic antagonist) and phentolamine (non-specific alpha adrenergic antagonist). The melanophore responses to repeated potassium stimulation (up to 20 stimuli) did not show any sign of fatigue. However, statistically significant enhancement was observed in responses to potassium that followed the first five stimulations. Adrenergic agonists acted in a time and concentration-dependent manner and their relative potency had the following rank order: clonidine (alpha-2 specific agonist) > norepinephrine (non-specific adrenergic agonist) > phenylephrine (alpha-1 specific agonist) > methoxamine (alpha-1-specific agonist). Yohimbine exerted a more potent inhibiting effect on norepinephrine induced melanosome aggregation compared to phentolamine. Prazosine (alpha-1 specific antagonist) had no effect on such aggregation. Chemically denervated melanophores displayed hypersensitivity to alpha-adrenergic agonists but were refractive to potassium ion stimulation. The refractivity of denervated melanophores to potassium indicates the effect of potassium ion is not direct on melanophores but it is rather through depolarization effect of potassium on the neuro-melanophore peripheral sympathetic fibers and hence release of norepinephrine. In denervated melanophores, similar to intact melanophores, only phentolamine and yohimbine but not prazosine, significantly inhibited melanosome aggregation effect of norepinephrine, indicating that norepinephrine effect is through postsynaptic alpha-2 adrenoceptors. The present data demonstrate that the nature of melanophore innervation in this teleost is adrenergic and neuro-melanophore signals mediating melanosome aggregation are transmitted through alpha-2 postsynaptic adrenoceptors.

Effect of feeding level & fish density on growth and food conversion of cultured white-spotted rabbitfish (Siganus cansliculatus Park,1797)

Effect of feeding level & fish density on growth and food conversion of cultured white-spotted rabbitfish (Siganus cansliculatus Park,1797)

Out-migration of Tagged Fishes from Marine Reef National Parks to Fisheries in Coastal Kenya

We evaluated movements of 25 species of coral reef fishes from Malindi and Watamu Marine National Parks (created 1968) in coastal Kenya from February 2001 to March 2002. Only three species, the commercially important whitespotted rabbitfish, Siganus sutor, the sky emperor (SEM), Lethrinus mahsena and the trumpet emperor, L. miniatus, exhibited consistent movements from the parks. At Malindi Park, more fishes were recaptured by fishermen off a fringing reef than off a patch reef. The rabbitfish had a higher monthly spillover rate from the fringing reef than from the patch reef. In contrast, the SEM had low monthly spillover rates from both reefs. The rabbitfish moved greater distances off the fringing reef than off the patch reef. At Watamu Park, the SEM, L. miniatus and the gold-spotted sweetlips, Gaterin flavomaculatus, had equal monthly spillover rates. In contrast, the rabbitfish had a lower monthly rate. The emperors showed no difference in net distance moved from the park boundary, however, L. miniatus traveled significantly longer distances than did the SEM. Distances between release and capture sites were either random (SEM), increasing (L. miniatus), or decreasing (rabbitfish) with respect to time at liberty.

Long-term Trends in Coral Reef Fish Yields and Exploitation Rates of Commercial Species from Coastal Kenya

Keywords: coral reef fish, yield, long term trends, commercial fishing, Kenya Analysis of long-term (1978–2001) marine fisheries data showed that Kenyan coralreefs produced an estimated 2–4 metric t/km2/year of demersal fish. A rapid overall decline in landings occurred during the 1990s. Yields (t/km2/year) showed bimodal peaks in 1982 (2.98) and 1991 (2.90). The average total landings dropped by 55% during the last decade following peak landings in 1982. Landings of the commercially important families (e.g., Siganidae, Lethrinidae, Lutjanidae and Serranidae) declined by about 40% during the last decade, with the groupers (Serranidae) showing the steepest (72%) decline. Analysis of landings per administrative district showed a 78% decline in the densely populated Mombasa district between the periods 1983–1991 and 1992–2001. The less populated districts have registered stable (e.g., Kilifi) to increasing (e.g., Kwale) catches over time. An autoregressive moving average (ARIMA) model forecast of landings predicted a gradual decline in catches during the next decade (2002– 2011) with a trend slope of -0.01 t/km2. Length-frequency analysis for the commercially important species indicated above optimum exploitation (E) and fishing mortality (per year) rates for the sky emperor, Lethrinus mahsena (E = 0.64; F = 2.48) and lower but strong rates for the emperor, L. sangueinus (E=0.51; F=0.93). The more abundant and commercially important whitespotted rabbitfish, Siganus sutor, showed equally strong rates (E= 0.56; F = 1.44/year). A precautionary approach in the management of Kenya\'s coral-reef fisheries is recommended. Western Indian Ocean Journal of Marine Sciences Vol.2(2) 2003: 105-116

Effects of marine reef National Parks on fishery CPUE in coastal Kenya

The role of marine protected areas in conserving fish stocks and their potential influence on adjacent fisheries was studied at Malindi and Watamu Marine National Parks, Kenya (established in 1968). For most species catch per unit effort (CPUE) in traditional Dema traps fished across park boundaries was higher within the parks (up to an order of magnitude). However, a few species (e.g., the seagrass parrotfish, Leptoscarus vaigensis and the whitespotted rabbitfish, Siganus sutor, WSR) had higher seasonal CPUE outside the parks. Potential spillover of fishes from the parks to adjacent fished areas was tested with a logistic “decay” model of density gradients (CPUE) across park borders from fringing and patch reefs. A steep decay in CPUE off the Malindi patch reef suggested little spillover of most species. However, greater spillover was suggested off fringing reefs. Species differences were evident. The two most important commercial species showed different density gradients. Species diversity declined more abruptly off the fringing reefs. We conclude that although spillover of most species from the parks is limited, the most important commercial species exhibits significant spillover to adjacent fisheries and the Parks likely comprise important nursery and growth areas for other species.

Streptococcus iniae, the Causative Agent of Mass Mortality in RabbitfishSiganus canaliculatusin Bahrain

Streptococcus iniae was found to be responsible for mass mortality in whitespotted rabbitfish Siganus canaliculatus in Bahrain. External signs were listless swimming and dark coloration. Internally, ascites, hepatomegaly, and splenomegaly were observed. Identification of the bacterium was based upon biochemical, physiological, serological tests and DNA–DNA hybridization. Host susceptibility was examined in five fish species. Rabbitfish was the species most susceptible to streptococcal infection. Borneo mullet Liza macrolepis and brown-spot grouper Epinephelus coioides were also susceptible to the bacterium, whereas the seabream Acanthopagrus latus (known in Bahrain as black seabream) and one-spot bream Diplodus sargus were not.

Breeding biology of rabbitfish Siganus canaliculatus (Siganidae) in mid Arabian gulf

The breeding cycle of the white-spotted rabbitfish Siganus canaliculatus Park in Dammam waters off the Saudi coast of the Arabian gulf was investigated. Spawning mainly occurred in April and May, when sexual products were released in batches. Maximum fresh ovum size was 360 μm. Sexual maturation was first attained at total lengths of about 17 cm for males and 17.5 cm for females at the beginning of the second year of life. The overall sex ratio was almost unity but males pre-dominated in the catch during the post-spawning period. S. canaliculatus is a highly fecund species producing up to a million eggs per female. Both absolute and relative fecundity were estimated and were closer related to fish weight rather than to length. There was a strong relationship between ovary weight and absolute fecundity.

Ectoparasites of the whitespotted rabbitfish, Siganus sutor (Valenciennes, 1835) off the Kenyan Coast: distribution within the host population and site selection on the gills.

Different populations of the whitespotted rabbitfish, Siganus sutor, were examined for ectoparasites: adults from the Mombasa area (sampled in December 1990) and different age classes (adult, subadult and juveniles) from Gazi Bay (sampled in December 1992 and August 1993). The most common gill parasites were: the monogeneans Pseudohaliotrema sp., Tetrancistrum sigani and Microcotyle mouwoi, the copepods Hatschekia sp., Pseudolepeophtheirus sp. and juvenile Caligidae, and prazina larvae of the isopod Gnathia sp. Adult siganids had a higher parasite load than subadults. Juvenile rabbitfish did not harbour any gill parasites. Temporal differences in the parasite load of subadult rabbitfish were observed for M. mouwoi (highest in the December samples) and for juvenile Caligidae (highest in August). The microhabitat of the 5 most common gill parasites was species specific. Most parasite species showed distinct site preferences with respect to both gill arches and gill sectors, within the gill arches. Niche breadth of the different gill parasite species was independent of the abundance of any of the other species present. However, niche breadths of M. mouwoi, Tetrancistrum sp. and Hatschekia sp. increased with their own abundance. This suggests that interspecific competition for space is low and that intraspecific factors could play an important role in the microhabitat choice of these gill parasites. The hypothesis that niche restriction leads to higher intraspecific contact and an enhancement of chances to mate was tested on 2 monogenean species, Pseudohaliotrema sp. and Tetrancistrum sigani. Their highly aggregated distribution over the gill filaments, leading to increased intraspecific contact, is consistent with the hypothesis.